1. Technical Field
The present invention generally relates to semiconductor devices and fabrication of the semiconductor devices. More particularly, the present invention relates to controlling gate height by reducing oxide recess and achieving gate height uniformity.
2. Background Information
Gate-first and Gate-last approaches have been two principle approaches for forming semiconductor device gate structures.
In a gate-first fabrication approach, a metal gate is provided over a gate dielectric, and then patterned and etched to form one or more gate structures. After forming the gate structures, source and drain features of the semiconductor devices are provided. In the gate-last approach, a sacrificial (or dummy) gate material is provided, patterned and etched to define one or more sacrificial gates. The one or more sacrificial gates are subsequently replaced with corresponding replacement metal gates, such as, for example, amorphous silicon (a-Si) or polycrystalline silicon, holds the position for the subsequent metal gate to be formed. For instance, an amorphous (a-Si) or polysilicon sacrificial gate material may be patterned and used during initial processing until high-temperature annealing to activate the source and drain features has been completed. Subsequently, the a-Si or polysilicon may be removed and replaced with the final metal gate.
During the fabrication process, a variety of gap fill materials such as, a flowable dielectric material (e.g. flowable oxide) are typically employed in the etched opening in the insulating layer between the adjacent gates, which would later be replaced by contact metal, during the subsequent fabrication processing. However, the quality of the gap fill may typically be poor and may be vulnerable to subsequent wet/dry etch processing. For example, when fabricating replacement metal gates with a tungsten metal gate, a sacrificial material is used between adjacent gate structures along with a fill material, such as a nitride over the entire structure. Subsequent chemical mechanical planarization of the tungsten and/or sacrificial nitride filler material may yield excessive recesses, particularly in the sacrificial material. Such recesses effect the resultant gate height.
Hence, there continues a need for a technique to control gate height, particularly due to oxidation recesses caused by processing of filler material.